As it is known, a telephone network such as the PSTN network (“Public Switched Telephone Network”) or the PLMN network (“Public Land Mobile Network”) generally comprises a plurality of exchanges interconnected by trunks. Exchange and trunk arrangements determine the network topology. A plurality of users may be connected to an exchange by means of respective terminals.
An exchange is in charge, inter alia, of routing calls from calling terminals to called terminals. More particularly, when a caller unhooks his terminal for making a call, the exchange to which the calling terminal (namely, the terminal of the caller) is connected detects the off hook condition of the calling terminal, and it sends it a dial tone. The caller then dials the callee number, i.e. the telephone number identifying the called terminal. The callee number may be transmitted to the exchange for instance through DMTF tones. Upon reception of the callee number, the exchange attempts to route the call towards the called terminal (possibly through other exchanges), by attempting to establish a connection between the calling terminal and the called terminal.
A connection may be either successfully established or not. In the affirmative, the call setup procedure is successful, while in the negative the call setup procedure is unsuccessful. In both cases, after the call setup procedure is concluded, an event indicating the end of the call setup procedure is generated by the telephone network, and a corresponding signaling message indicating the end of the call setup procedure is sent backward from the exchange which generated the event. The expression “signaling message” refers in general to a message which comprises measurement information generated by an exchange during a given measurement period. A signaling message may be formatted according to any known signaling protocol such as ISUP, SIP or the like.
The signaling message indicating the end of the call setup procedure is called “end of selection” signal (or briefly, EOS signal).
An EOS signal is generated by the telephone network for indicating the outcome of a call setup procedure, i.e. for indicating the successful completion or unsuccessful termination of the call setup procedure, and it may contain information of the called party's line condition.
In case of a successful call setup procedure, a “normal” EOS event is generated, and the conversation between the caller and the callee may begin. On the contrary, in case of unsuccessful call setup procedure, e.g. due to a congestion or a failure of the telephone network or due to the fact that the callee is already engaged in another call, an EOS event of a type other than “normal” is generated. The EOS event type mainly depends of the reason why the setup procedure is unsuccessful.
Known exchanges have an EOS processing function for processing EOS events received by other exchanges and performing consequent actions. For instance, in case of an unsuccessful call setup procedure due to the fact that there are no free resources in the network, e.g. no trunk available, an EOS event of “congestion” type is generated. When the exchange to which the calling terminal is connected receives such a “congestion” EOS event, it processes it by its EOS processing function, which recognizes the “congestion” EOS event and then establishes to send a congestion tone to the calling terminal and to release the connection. Typically, for each type of EOS event, the EOS processing function of an exchange counts the number of received EOS events of that type by means of a respective counter.
The number of unsuccessful call setup procedures in a telephone network affects the quality of service of telephone services provided by a network provider through the telephone network. In particular, a network provider would have to minimize the ratio between the number of unsuccessful call setup procedures and the overall number of call requests.
Different methods are known in the art for monitoring the performance, or quality of service, of a telephone network.
U.S. Pat. No. 6,914,967 describes a method for assessing the quality of service of telephone calls on a trunk by identifying and counting telephone call sequences including a plurality of telephone calls placed on the trunk by analyzing CDRs. Each of the telephone calls in the sequence has the same originating telephone number and the same destination telephone number and a start time and a stop time and an elapsed time between the stop time of a telephone call and the start time of the next telephone call in a sequence being less than a predetermined amount. Identifying and counting unanswered reattempted telephone calls or answered reattempted telephone calls. A ratio is calculated between the number of identified unanswered or answered reattempted telephone calls to the number of identified telephone call sequences, such that the ratio provides a measure of the quality of service of telephone calls on the trunk.
WO 0120920 discloses a method for monitoring service quality using Call Detail Records (CDR) in a communications network, such as an SS7 network. Network monitors capture substantially all signaling units in the SS7 network and generate a complete record for all calls, transactions and other communications over the network. Users configure CDR profiles that are used to filter the records. A CDR application filters the records by parsing out signaling unit components that have been selected by the user in the CDR profile. The selected message components are then formatted into a CDR record, which is sent to an external system that generates certain statistics for the message records and stores the statistics to a database. A report application recalls the statistics from the database and presents statistics in a reporting format configured by the user. The reports indicate the statistical performance of network providers for selected called or calling telephone numbers or for selected services. The CDRs and statistics are available to a user either in real-time or in response to a query of historical CDR data.
U.S. Pat. No. 6,381,306 describes a method for generating service quality statistics for a communications network. Network monitors capture messages in a communications network, such as an SS7 network, and correlate related messages into records. The records are filtered using a call detail record profile to create call detail records which are provided to a statistics server. The statistics server generates certain statistics for the message records and stores the statistics to a database. A report application recalls the statistics from the database and presents statistics in a reporting format configured by the user. The reports indicate the statistical performance of network providers for selected called or calling telephone numbers or for selected services.
U.S. Pat. No. 6,529,594 discloses a method for capturing signaling units at international gateways in a communications network. The signaling units are processed to determine the source and destination networks for the associated calls. The country code, nature of address field, destination point code and origination point code is used to process each message. Data about the messages that pass through the international gateway is stored to a memory device. The data can be recalled for each originating or destination network in the form of performance or quality of service statistics.